... 2 * Evolution MK-261 keyboard controllers for the manuals, + a midi pedalboard from Classic Organs. I am merging up the 3 midi signals via 2 * Phil Ress Little 2M midi merge units connected in series ... into the single midi-in on my Soundblaster Audigy card.
Since adding in the additional manual (and a second midi merge unit), once or twice an hour I am getting cyphering and I can only release the affected notes by resounding the affected notes or doing a Hauptwerk “Reset All Notes”....
I've had and sometimes have a similar problem.
I have the Classic Organ Works pedalboard and 3 keyboard stack and am using a MIDISPORT 2x2 that I borrowed from a friend. (Previously I was using my SoundBlaster MIDI in and an Evolution MK-361C controller.)
Classic Organ Works products have built in MIDI merging. Oddly enough I was unable to combine / merge the keyboard stack with the pedalboard. I couldn't get them to work at all with my SoundBlaster MIDI and was using a MIDISPORT 1x1 for the pedalboard and the SoundBlaster for my Evolution keyboard. When the keyboard stack arrived I had frequent cipher problems, using their built in MIDI merge and finally borrowed a 2x2 from a friend.
Had I only known I would have bought the MTU 5x5 which is about the same price or cheaper than the MIDISPORT 4x4.
Merging "should" work but, I agree, separate interfaces are best. I'm using the built it Classic Organ Works merging for the 3 manual keyboard stack and am using a separate channel for the pedalboard. Once in awhile I get a cipher that is impossible to reproduce.
I suppose the cipher is good practice for my church's 1923 Kilgen that has 3 ciphers on the Swell.
If you get a 4x4 or 5x5 interface you'll be better off.
IMHO